irda: net/irda build fix: mcs7780

-tip testing found the following build error:

  drivers/built-in.o: In function `mcs_receive_irq':
  mcs7780.c:(.text+0x4e429): undefined reference to `crc32_le'
  drivers/built-in.o: In function `mcs_hard_xmit':
  mcs7780.c:(.text+0x4e9af): undefined reference to `crc32_le'

with:

  http://redhat.com/~mingo/misc/config-Sun_Jun__8_22_56_14_CEST_2008.bad

the reason is a missing enablement of the CRC32 library in the Kconfig.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>